1. Field of the Invention
The present invention relates to photoelectric input apparatus; more particularly, to touch input panels having a series of crossed light beams, in which the interruption of a pair of crossed light beams identifies the position of an object in the plane.
2. The Prior Art
Photoelectric touch input panels have been developed which use a plurality of crossed light beams, arranged in sets of parallel beams in a single plane, to identify the approximate position of an object which breaks both of two crossing beams. Typically, such touch input panels are intended to be used in front of a display device such as a cathode ray tube, and the position of an operator's finger when it touches a spot on the cathode ray tube is detected by determining which two crossed beams are simultaneously interrupted. At times, the touch input panel is used with a stylus or other device in place of a finger. The resolution with which the position of the finger or stylus can be determined is dependent largely upon the spacing of the parallel beams in the beam plane and the width of the finger or stylus. The beams must be spaced apart by a distance which is small enough to insure breaking at least one beam by the smallest size finger or stylus, and, accordingly, it is frequently the case that multiple beams are broken. In previous touch input panels, the output is produced by an indication of the first beam which is recognized as being broken, scanning from one direction toward the other (for example, from the top down), and this results in determination of a position which is not the position corresponding to the center line of the finger or stylus. Accordingly, it is desirable to provide a way of determining the approximate center point of the finger or stylus if more than one of a series of parallel beams is broken.
In previous touch input panels, it is possible for a relatively small foreign object, such as an insect, a raindrop or debris, to cause a false indication of an input by passing through the beam plane. It is, therefore, desirable to provide a mechanism for discriminating against foreign objects which happen to pass through the beam plane of the device.
In previous touch input panels, a relatively complicated arrangement is required for controlling operation of the panel. It is desirable to simplify, as much as possible, the logic and electronic circuits required in the use of the panel to enable the panel to be produced with as much economy as possible, and to increase the reliability of the panel.
Previous touch input panels, while useful for determining the position of an object in a beam plane, are not capable of sensing any additional data relating to such input, such as the velocity of approach of the object toward the touch panel. It is sometimes desirable to be able to discriminate the velocity of approach of an object which intersects the beams in the beam plane, in order to insure with greater certainty that an actuation of the touch input panel is an intentional actuation by means of a finger or stylus, rather than an accidental operation. It is, therefore, also desirable to provide some means of sensing the velocity of approach of an object which intersects the beams and the beam plane.
Previous touch input panels are adapted to scan through the entire population of each set of beams on a sequential basis, and therefore each individual beam is scanned relatively infrequently. This establishes a time interval of uncertainty as to whether a beam is interrupted or not. It is desirable to reduce this time interval, and increase the scanning rate for one or more specific beams which are of greater significance, or which are more likely than others to be interrupted.
Previous touch panels are not well-adapted to operation in more than one mode. Typically, they operate in a point mode, in which points are identified by decoding the X-Y coordinates of a broken beam pair, without recognizing additional points which may be legitimate inputs until after a condition is recognized in which no beam is broken. It is desirable to avoid this limitation and permit multi-mode operation of the touch panel.
Previous touch panels have not been well-adapted to recognize and detect more than one pair of interrupted beams at a time, which severely limits the usefulness of the panel. It is desirable to provide an arrangement in which a number of interrupted crossed beam pairs are recognized. This makes it possible to use touch input panel control apparatus to perform a variety of tasks such as sizing, space monitoring, and protection interlock activities.
Previous touch panels have not been able to discriminate between touch inputs (by a finger or stylus) which move normally to the touch panel. It is desirable to be able to distinguish between normal or skew approaches, particularly in applications where high resolution of the touch input is required.
Previous touch panels have been required to use comparators for determining, in each beam plane, whether a beam detected as being interrupted is different from the last detected beam. It is desirable to provide an arrangement which makes the use of such comparators, and other associated logic, unnecessary.